The SO2 emitted from coal-fired power plants is the main source of atmospheric pollutants and the primary cause of acid rain. With advantages of technical maturity, high desulfurization rate, reliable operation and comprehensively utilizable side products, wet limestone-gypsum flue gas desulfurization technology has been the most widely used flue gas desulfurization technology in the world.
Due to market changes, the fire coals actually used in thermal power plants which can be obtained from a wide diverse sources containing a variety of impurities, the sulphur content of the actually used fire coals is significantly different from the designed one, and the characteristics and the SO2 content of flue gas fluctuate widely, leading to the overloaded operation of a desulfurization system, the likely foaming of slurry, the decrease of the pH value of slurry and the reduction of desulfurization rate, which severely influences the up-to-standard emission of SO2 in flue gas.
To control the emission of nitric oxides in flue gas of thermal power plants, some of thermal power plants are equipped with a flue gas denitration system, and the common flue gas denitration technology is a selective catalytic reduction (SCR) technology according to which a great amount of metal oxide catalyst is needed to oxidize the SO2 in flue gas into SO3 which forms tiny sulfuric acid mist that cannot be removed by using a wet limestone-gypsum flue desulfurization technology, which causes the corrosion of a downstream device and the emission of acid mist.